1. Field of the Invention
The present invention relates to ships including motorboats, pleasure boats, passenger ships, cargo ships, warships, and boats with outboard motors, and more particularly, to a ship with improved propulsive performance in order to save energy and with improved steering performance, and also to a rescue boat whose navigation is not hindered by floating matters on the water, obstacles in the water or the like.
2. Description of the Related Art
An existing ship has a propulsion propeller (screw propeller) and a rudder exposed at the back of hull's bottom, which has not changed basically ever since the ship began to propel with power. Meanwhile, many proposals have been made to improve the propulsive performance and the steering performance, examples of which will be presented as follows.
Improvement in Propulsive Performance
Japanese Unexamined Patent Application Publication No. 2011-225169 discloses a ship having a stern pipe in a stern, the stern pipe being projected from the stern toward the back of a hull, and rotatably supporting a rotary shaft of a propeller. The ship includes fins that are disposed on right and left sides of the stern, extended toward the outside of hull width direction and toward the upside of the hull from the stern near the stern pipe, and shield stern vortices S generated at the stern in radial direction from vortex centers X of the stern vortices S.
Japanese Unexamined Patent Application Publication No. 2011-140293 discloses a propulsion performance improving device for a ship having a superior effect with comparatively simple constitution, which can improve propulsion efficiency by increasing swirling water flows in direction opposite to propeller advancing rotating direction to allow the swirling water flows to flow in the propeller and to reduce rotating flows on a rear side of the propeller, and can prevent an increase in drag of the device itself. This propulsion performance improving device includes rear fins having twisting angles larger than those of conventional fins, and front fins located in a front region and having twisting angles smaller than those of the conventional fins. Drag of the front fins and the rear fins is not increased as compared with the conventional fins, and a reduction effect of a propeller real' rotating flow is increased. As a result, the ship has better propulsion performance improving effect than that of the conventional ship, and less horsepower is required when the hull is navigated.
Japanese Unexamined Patent Application Publication No. 2011-121569 discloses a propulsion performance improving device of a ship capable of preventing a propeller from being damaged by a vortex generated by reaction fins. This propulsion performance improving device for improving propulsion performance of the ship includes a plurality of reaction fins that are arranged on a front side of the propeller to generate a swirling flow in direction opposite to rotational direction of the propeller, and that are radially extending with a rotary shaft S of the propeller as the center. The plurality of reaction fins include the reaction fin extending in obliquely upward direction and the reaction fins extending in horizontal direction or obliquely downward direction. A first distance to a blade end of the reaction fin from the rotary shaft S is larger than a propeller radius of the propeller. A second distance to a blade end of the reaction fin from the rotary shaft S is set to be smaller than the propeller radius.
Improvement in Steering Performance
Japanese Unexamined Patent Application Publication No. 2009•119934 discloses a ship rudder for enhancing course keeping performance of a ship by reducing rudder drag during forward movement of the ship with a simple method and reducing meeting rudder drag in a minute steering angle as small as possible, by improvement of a lower end of a conventional ship rudder having an inverted trapezoidal side shape. The rudder at a stern is equipped with an additive object, as being a flat spindle body having an airfoil vertical cross section slightly projecting outward, on a lower end of the rudder body having the inverted trapezoidal side shape. A center line of a vertical cross section of the additive object is inclined backward and obliquely upward, and an inclination angle a is set to be 4 to 10 degrees. Then, the additive object receives a stream toward a rear side of a ship's bottom near the rudder during navigation, so as to generate lift. As its forward component acts as thrust, the rudder drag can be reduced, and improved steering force can be expected at the time of steering.
Japanese Unexamined Patent Application Publication No. 2007-186204 discloses a rudder that has high lift and suppresses increase in rudder drag as small as possible. 'Ib obtain such a rudder, a horizontal cross section of a rudder body has an arc or similar shape at a front end portion. Its sectional width gradually increases toward a rear side of the rudder body, reaches the maximum width, and then, gradually decreases while changing from an outwardly projecting shape to an outwardly and gently recessed shape. Then, the rudde1′ has a linear portion formed by approximately parallel lines continuing to the rear end of a finite width.
Japanese Unexamined Patent Application Publication No. 2005-246996 discloses a ship rudder capable of improving propulsive performance by efficiently converting rotational energy of a propeller wake at a shaft into lift, and improving rudder performance by increasing a rudder area. In the rudder arranged on a rear side of the propeller of a ship, fins to generate the lift from the propeller wake are provided on a front side or an obliquely front side of a rudder body with a space S in which the propeller wake flows between the propeller and the rudder body, so that span direction of the fins becomes vertical to the rudder.
According to the above described means for improving the propulsive performance, however, the propeller is entirely located in the water. With regard to drag acting on the propeller, thrust produced by the propeller is substantially reduced because the thrust is diminished and the thrust toward the rear side is dispersed by receiving wave drag.
Next, according to the above described means for improving the steering performance, water drag acting on the rudder becomes the steering force. The rudder is also entirely located in the water, and therefore it is impossible to obtain the sufficient steering force because of dispersion of the steering force in the surrounding water, the steering force being produced by making contact with water and determining the direction.
The above-described problems are challenges for the ships through all ages. In spite of various improvements and proposals made thus far, no conclusive proposal has been made up to the present date.
With the conventional ships such as rescue boats and boats with outboard motors, it may be difficult to approach its destination because there is a risk of damaging propellers and rudders due to floating matters on the water and rocks in the shallows.
With the boats with the outboard motors, the boat usually has a spare outboard motor because it cannot sail back home once the outboard motor is broken. However, there is a problem that replacement of the spare outboard motor takes time and effort especially when being alone. With the boats with the outboard motors, the propeller becomes obstructive when pulling the boat onto the ground (beach) and letting it down into the sea. Therefore, the outboard motor needs to be put on board each time, which is quite bothersome.